Rotor for permanent magnet motor of outer rotor type

ABSTRACT

A rotor for a permanent magnet motor of an outer rotor type having a plurality of permanent magnets and disposed around a stator includes a frame, an annular iron core combined integrally with the frame, and a plurality of insertion holes formed in the core so that the permanent magnets are inserted in the insertion holes respectively. The frame, the core and the permanent magnets are combined integrally with one another by a synthetic resin. Each insertion hole includes a magnet disposing portion in which the permanent magnet is disposed, a space portion located in at least one of circumferential both ends of each permanent magnet disposed in the magnet disposing portion, and a positioning portion positioning each permanent magnet in the magnet disposing portion, and the molten synthetic resin is poured into the space portion.

BACKGROUND OF THE INVENTION

This is the U.S. National Stage of International Application No.PCT/JP03/07631, filed on Jun. 16, 2003, which relies for priority onJapanese Patent Applications Nos. 2002-179785. filed Jun. 20, 2002 and2002-310967, filed Oct. 25, 2002, the contents of all of which areincorporated herein by reference in their entireties.

1. Field of the Invention

This invention relates to a rotor for a permanent magnet motor of theouter rotor type which includes a number of annularly arranged permanentmagnets for formation of magnetic poles.

2. Description of the Related Art

FIGS. 18 and 19 illustrate a part of a rotor for a conventionalpermanent magnet motor of the outer rotor type in which a rotor isdisposed around a stator. As shown, a rotor 10 comprises a frame 1 madefrom a magnetic material and including a disc-like main plate 1 a and anannular circumferential wall 1 b located around the main plate 1 a, anda plurality of permanent magnets 2 arranged on an inner circumferentialface of the wall 1 b for the purpose of forming magnetic poles. A ringmember 4 made from a magnetic material is disposed along an outercircumference of the wall 1 b. The aforesaid frame 1, permanent magnets2 and ring member 4 are integrally combined with one another by asynthetic resin 5. For example, Japanese Patent No. 3017953 discloses arotor with the above-described construction.

The above-described rotor 10 is manufactured in the following method. Aforming die 6 includes a lower die 6 a and an upper die 6 b as shown inFIG. 20A. The permanent magnets 2 are inserted into a recess 7 formed inthe lower die 6 a. The recess 7 is formed into an annular configurationaccording to a shape and the number of the permanent magnets 2. Theframe 1 is then put over the permanent magnets 2 inserted in the recess7, and the ring member 4 is further disposed along the outercircumference of the frame.

Subsequently, the upper die 6 b is put onto the lower die 6 a so thatthe forming die 6 is closed as shown in FIG. 20B. A cavity 8 definedbetween the upper and lower dies 6 b and 6 a is filled with a syntheticresin 5 in the molten state. When the synthetic resin 5 has beenhardened, the upper die 6 b is removed and the rotor 10 is taken fromthe lower die 6 b. Thus, a number of permanent magnets 2 are integrallycombined with the frame 1 by the synthetic resin in the annularlyarranged state.

In the above-described rotor 10, however, the recess 7 needs to beprovided in the lower die 6 a in order that the permanent magnets 2 maybe prevented from being displaced during filling the interior of the die6 with the synthetic resin 5. Accordingly, the configuration of thelower die 6 a is complicated.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a rotor forthe permanent magnet motor of the outer rotor type which can simplifythe configuration of the forming die.

The present invention provides a rotor for a permanent magnet motor ofan outer rotor type, the rotor having a plurality of permanent magnetsand disposed around a stator, the rotor comprising a frame, an annulariron core combined integrally with the frame, and a plurality ofinsertion holes formed in the core so that the permanent magnets areinserted in the insertion holes respectively, wherein the frame, thecore and the permanent magnets are combined integrally with one anotherby a synthetic resin, and each insertion hole includes a magnetdisposing portion in which the permanent magnet is disposed, a spaceportion located in at least one of circumferential both ends of eachpermanent magnet disposed in the magnet disposing portion, and apositioning portion positioning each permanent magnet in the magnetdisposing portion, and the molten synthetic resin is poured into thespace portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a permanent magnet motor ofthe outer rotor type in accordance with a first embodiment of thepresent invention;

FIG. 2 is an enlarged cross-sectional view of a part of the rotor;

FIG. 3 is a longitudinal section of the rotor taken along line 3—3 inFIG. 2;

FIG. 4 is a longitudinal section of the rotor taken along line 4—4 inFIG. 2;

FIG. 5 is a plan view of the overall rotor;

FIG. 6 is a perspective view of a part of the rotor;

FIG. 7 is a perspective view of a frame;

FIG. 8A shows a step of disposing components of the rotor in a formingdie;

FIG. 8B shows a step of pouring molten resin into the forming die;

FIG. 9 is a view similar to FIG. 2, showing the rotor of the permanentmagnet motor in accordance with a second embodiment of the present;

FIG. 10 is a perspective view of the overall rotor in accordance with athird embodiment of the present invention;

FIG. 11 is a view similar to FIG. 2;

FIG. 12 is a longitudinal section of the rotor taken along line 12—12 inFIG. 11;

FIG. 13 is a longitudinal section of the rotor taken along line 13—13 inFIG. 11;

FIG. 14 is a view explaining the magnetic flux distribution;

FIG. 15 is a view similar to FIG. 10, showing a fourth embodiment of thepresent invention;

FIG. 16 is a view similar to FIG. 10, showing a fifth embodiment of thepresent invention;

FIG. 17 is a view similar to FIG. 14, showing a sixth embodiment of thepresent invention;

FIG. 18 is a longitudinal section of a part of the rotor of aconventional permanent magnet motor of the outer rotor type;

FIG. 19 is a cross-sectional view of a part of the rotor;

FIG. 20A is a view similar to FIG. 8A; and

FIG. 20B is a view similar to FIG. 8B.

DESCRIPTION OF THE INVENTION

A first embodiment of the present invention will be described withreference to FIGS. 1 to 8. Referring to FIG. 1, a permanent magnet motor100 of the outer rotor type is shown. The motor 100 comprises a stator11 and a rotor 16. The motor 100 is mounted, for example, on a rear wallof a water tub constituting a washing machine to direct drive a rotatingtub.

The stator 11 includes an annular yoke 12 a and a stator core 12 havinga number of teeth 12 b projecting radially outward from an outercircumference of the yoke 12 a. The stator core 12 is made, for example,by laminating a number of silicon steel sheets stamped out into apredetermined configuration. A covering member 14 made of an insulatingresin is provided substantially over entire outer faces of the yoke 12 aand teeth 12 b by means of molding. A plurality of mounting portions 15are provided integrally on the covering member 14 so as to be located onan inner circumference of the yoke 12 a. The mounting portions 15 areused for mounting the stator 11 on a rear wall (not shown) of a watertub of a washing machine. A coil 13 is wound on the covering member 14covering each tooth 12 b. Thus, the stator 11 is constructed asdescribed above. On the other hand, the rotor 16 includes a frame 17 anda rotor core 18 both formed integrally from a synthetic resin 35 (seeFIGS. 2 to 4).

The frame 17 is made by pressing a magnetic material such as steel sheetinto the shape of a bottomed flat cylinder. The frame 17 includes a mainsheet portion 17 a having a central shaft-supporting mounting hole 20and an annular wall 17 b standing at an outer circumferential edge ofthe main sheet portion 17 a. A shaft support (not shown) supporting arotational shaft is adapted to be mounted in the mounting hole 20. Therotational shaft is rotatably mounted on bearings (not shown) A steppedportion 21 is provided along an overall outer circumference of the mainsheet portion 17 a. The rotor core 18 is disposed in a space defined bythe stepped portion 21 and an annular wall 17 b. In this case, innercircumferential faces of the rotor core 18 and stepped portion 21 arerendered substantially coplanar. The stepped portion 21 has a pluralityof through holes 22 formed along an overall circumference thereof. Themain sheet portion 17 a has a number of vent holes 23 which are formedin a portion thereof between the mounting hole 20 and the steppedportion 21 so as to be arranged radially about the mounting hole.

The rotor core 18 is made by laminating a large number of sheets ofannularly punched magnetic material such as steel sheets. The rotor core18 has a number of insertion holes 25 formed therein. Permanent magnets19 for forming magnetic poles are provided in the insertion holes 25respectively. A plurality of steel sheets composing an upper end of alaminate of steel sheets have no insertion holes 25. Accordingly, theinsertion holes 25 are open at a lower end of the rotor core 18 but areclosed at the upper end of the rotor core.

Each insertion hole 25 includes a rectangular narrow portion 25 aextending tangentially with respect to the core 18 and a wide portion 25b. The wide portion 25 b is located at the outer circumferential side ofthe core 18 and has a recess 27 formed at a central outercircumferential portion thereof and having a generally semicircularsection. Distance B from the wide portion 25 b to the outercircumference of the core 18 is set to be longer than distance A fromthe narrow portion 25 a to an inner circumference of the core 18.

Each permanent magnet 19 is formed into the shape of a rectangular plateand has a length that is substantially the same as a circumferentiallength of the narrow portion 25 a. Each permanent magnet 19 occupies anoverall narrow portion 25 a and a part of the wide portion 25 b.Accordingly, both circumferential ends and an outer circumferentialportion of each wide portion 25 b have a space where no permanent magnet19 is located. In the embodiment, the aforesaid overall narrow portion25 a and part of the wide portion 25 b serve as a magnet location. Astepped portion 26 between the narrow and wide portions 25 a and 25 bserves as a positioning portion. Each employed permanent magnet 19 is ofa high energy product type having a magnetic force not less than 2370MA/m. Each permanent magnet 19 is magnetized in the direction ofthickness thereof.

The rotor core 18 has a plurality of arc convex portions 30 formed on aninner circumferential face thereof. Each arc convex portion 30 is formedso that radial dimensions thereof at both circumferential ends thereofare smaller than a radial dimension thereof at the center thereof. Eachtrough 29 is located at the outer circumferential side relative to aradial center O at a portion thereof where a maximum radial dimension isachieved. Furthermore, the rotor core 18 has a plurality of throughholes 28 formed so as to be located at an outer circumferential siderelative to the respective troughs 29 and so as to extend axiallytherethrough.

Referring now to FIGS. 8A and 8B, a method of manufacturing the rotor 18is shown. A forming die comprises a lower die 32 a and an upper die 32b. The lower die 32 a includes a convex portion 33 in compliance withthe shape of the rotor 16. More specifically, the rotor core 18 isdisposed along an outer circumference of the convex portion 33 of thelower die 32 a after the permanent magnet 19 has been inserted in theinsertion hole 25. The frame 17 is then placed on the rotor core 18, andthe upper die 32 b is placed on the frame 17 so that the die is closed.Subsequently, a molten synthetic resin 35 is poured into a cavity 34defined by the upper and lower dies 32 b and 32 a. Consequently, themolten synthetic resin fills the through holes 28, the wide portions 25b of the insertion holes 25, the recesses 27 and the troughs 29. Thatis, the through holes 28 serve as passages for the molten resin 35.Parts of the wide portions 25 b where no permanent magnets 19 areprovided also serve as passages for the molten resin 35. Additionally,the molten resin 35 penetrates through the holes 22 outside the frame17.

Furthermore, the wide portion 25 b and the recess 27 are filled with themolten resin 35 such that each permanent magnet 19 is put aside to theinner circumferential end face of the insertion hole 25. In other words,the permanent magnet 19 is positioned in the narrow portion 25 a of theinsertion hole 25. Additionally, the molten resin 35 is formed into aplurality of ribs radially extending around the mounting hole 20 of theframe 17 as shown in FIG. 5. The upper die 32 b is then removed when themolten resin 35 has been hardened, and the rotor 16 is removed from thelower die 32 a. Thus, the rotor 16 in which the frame 17, rotor core 18and permanent magnets 19 are integrally combined together is made.

The permanent magnets 19 are inserted in the insertion holes 25respectively in the foregoing embodiment. Accordingly, the forming die32 requires no recesses to position the permanent magnets 19.Consequently, since the construction of the forming die is simplified,the cost of the product can be reduced. Furthermore, the convex portions30 are formed on the inner circumferential face of the rotor core 18,and an air gap between the rotor core 18 and the stator 1 is graduallyincreased from the central portion of the magnetic pole toward bothcircumferential ends. Accordingly, the magnetic flux density between thestator and rotor cores 12 and 18 is gradually decreased from the centralportion of the magnetic pole toward both circumferential ends, whereuponthe distribution of magnetic flux density is approximated to asinusoidal waveform. Consequently, the cogging torque can be reduced andaccordingly, the motor characteristics can be improved and amounts ofoscillation and noise can be reduced.

The troughs 29 are formed between the adjacent magnetic poles of therotor core 18. Consequently, the magnetic flux flowing between thepermanent magnets 19 can be prevented from shorting. In other words, themagnetic flux flowing between the permanent magnets 19 adjacent to eachother can be caused to pass to the outer circumferential portion of therotor core 18. Furthermore, the synthetic resin 35 fills the throughholes 28 and the troughs 29. Accordingly, the frame 17, the rotor core18 and the permanent magnets 19 are combined together more firmly.Moreover, the through holes 28 are formed in the outer circumferentialside of the core 18. Accordingly, the flow of magnetic flux from thepermanent magnets 19 to the stator 11 is not blocked and a reduction inthe motor characteristics due to provision of the through holes 28 canbe prevented.

Additionally, the distance B from each insertion hole 25 to the outercircumference of the core 18 is set to be longer than the distance Afrom each insertion hole 25 to the outer circumference of the core 18.Consequently, a sufficient passage for the magnetic flux can be ensuredin the outer circumference of the core 18 and accordingly, the flow ofmagnetic flux between the adjacent permanent magnets 19 can be improved.

FIG. 9 illustrates a second embodiment of the invention. Only thedifference of the second embodiment from the previous one will bedescribed. Identical or similar parts in the second embodiment arelabeled by the same reference symbols as those in the first embodiment,and the description of these parts will be eliminated. In the secondembodiment, the rotor core 18 comprises a plurality of unit cores 18aconnected one to another into an annular configuration.

The magnetic force is reduced since the magnetic resistance is increasedat connected portions 41 of each unit core 18 a. Accordingly, therotational speed of the rotor 16 is reduced near the connected portions41 in the construction of feedback control of the motor. A current valueand a voltage value are increased so that the rotational speed of therotor is increased. Thus, in the above-described arrangement, arotational position of the rotor 16 can be detected by measuring thecurrent and voltage values.

Additionally, a material for the core 18 can efficiently be used.

FIGS. 10 to 14 illustrate a third embodiment of the invention. Only thedifference of the third embodiment from the first embodiment will bedescribed. The rotor 16 of the second embodiment includes a frame 52 anda rotor core 53 both integrated by molding. The frame 52 is made bypressing a magnetic material such as a steel sheet into the shape of abottomed flat cylinder. The frame 52 includes a main sheet portion 55having a central shaft-supporting mounting hole 54 and an annular wall56 standing at an outer circumferential edge of the main sheet portion55.

A stepped portion 57 is provided along an overall outer circumference ofthe main sheet portion 55. The rotor core 53 is disposed in a spacedefined by the stepped portion 57 and an annular wall 56. In this case,inner circumferential faces of the rotor core 53 and stepped portion 57are rendered substantially coplanar. The stepped portion 57 has aplurality of through holes 58 formed along an overall circumferencethereof. The main sheet portion 55 has a number of vent holes 55 a whichare formed in a portion near the inner circumference thereof by cuttingand raising so as to be arranged radially about the mounting hole 12.

The rotor core 53 is made by laminating a large number of sheets ofannularly punched magnetic material such as steel sheets. The rotor core53 has a number of generally V-shaped insertion holes 59 formed therein.Pairs of permanent magnets 60 for forming magnetic poles are provided inthe insertion holes 59 respectively. Each pair of permanent magnets 60constitute magnetic poles in the embodiment.

Each insertion hole 59 has a central bent portion located at the outercircumferential side of the rotor core 53 and both circumferential endslocated at the inner circumferential side of the rotor core. Eachinsertion hole 59 is open at the outer circumferential face of the rotorcore 53. Of the laminated steel sheets composing the rotor core 53, oneor a plurality of steel sheets located at both axial ends have noinsertion holes 59. Accordingly, both axial ends of each insertion hole59 are closed.

Each permanent magnet 60 has the shape of a rectangular flat plate. Eachpair of permanent magnets 60 are contained in a storage section 59 aextending from the bent portion to one end of the insertion hole 59 anda storage section 59 b extending from the bent portion to the other endof the insertion hole respectively. Each storage section 59 a or 59 bhas a recess 61 formed in a central outer periphery so as to extend fullaxial length of the rotor core 53 and having a generally semicircularsection. The permanent magnets 60 are inserted through an opening 59 cof each insertion hole 59 into the storage sections 59 a and 59 b at theouter circumferential face of the rotor core 53 respectively. In thiscase, the recesses 61 are not occupied by the permanent magnets 60 andaccordingly serve as spaces.

Each employed permanent magnet 60 is of a high energy product typehaving a magnetic force not less than 316 MA/m. Each permanent magnet 60is magnetized in the direction of thickness thereof. Each pair ofmagnets 60 are contained in the storage sections 59 a and 59 b so thatinner circumferential side faces thereof have the same polarity.Furthermore, the rotor core 53 has axially extending circular throughholes 62 located between the insertion holes 59 adjacent to each other.The rotor core 53 further has semicircular notches 63 which are formedin the outer circumferential face thereof so as to be located betweenthe insertion holes 59 adjacent to each other.

In forming the rotor 16, molten resin 35 is poured into the spacebetween the annular wall 56 and stepped portion 57 of the frame 52 andthe rotor core 53 and hardened so that the frame and the rotor core areintegrated. In this case, the synthetic resin 35 flows through the holes58 to be located outside the frame 52. Furthermore, the molten resin 35also fills the through holes 62 and the notches 63. Thus, the rotor core53 is firmly fixed to the frame 52.

The molten resin 35 further flows through the openings 59 c into theinsertion holes 59, whereupon the permanent magnets 60 are pushedagainst the inner peripheral ends of the storage sections 59 a and 59 bthereby to be positioned. The resin 35 having flown into each insertionhole 59 further flows through gaps between the permanent magnets 60 andthe storage sections 59 a and 59 b into the recesses 61, whereupon thepermanent magnets 60 are pushed against the inner faces of the storagesections 59 a and 59 b located opposite the recesses 61 respectivelythereby to be positioned. Thus, in the embodiment, a portion of eachstorage section 59 a or 59 b except a portion filled with the resin 35serves as a magnet disposing portion.

The operation of the foregoing rotor will now be described withreference to FIG. 14 illustrating magnetic flux emerging from andre-entering the permanent magnets 60. The inner circumferential side(stator side) of the rotor core 53 is shown as the lower side as viewedin FIG. 13.

Since the permanent magnets 60 are disposed so as to obliquely cross theinterior of the rotor core 53 in the embodiment, the direction ofmagnetic flux Φ emerging from and re-entering the permanent magnets 60is inclined circumferentially. As a result, since a path of magneticflux re-flowing between the adjacent magnetic poles is mainlyestablished inside the rotor core 53, no magnetic path need beestablished in the annular wall 56 of the frame 52. Accordingly, thethickness of the annular wall 56 is enough to ensure the mechanicalstrength required to support the rotor core 53. Thus, the thickness ofthe annular wall 56 can be reduced as compared with the prior art andaccordingly, the weight of the rotor can be reduced.

Furthermore, magnetic flux Φ flowing in the inner circumferential sideof the rotor core 53 relative to the permanent magnets 60 is directed tothe central magnetic pole. Accordingly, the magnetic flux densitybecomes higher in the central portion than in the ends. Consequently,since the magnetic flux density distribution in a core gap approximatesto a sinusoidal waveform, the motor characteristics can be improved withreduction in the cogging torque.

In the third embodiment, the V-shaped insertion holes 59 are formed inthe rotor core 53, and two permanent magnets 60 constituting themagnetic poles are contained in each insertion hole 59. The magneticdirection of each magnet 60 is inclined circumferentially. Accordingly,since the annular wall 56 of the frame 52 need not serve as a back yoke,the thickness of the annular wall 56 can be reduced accordingly.Furthermore, two permanent magnets 60 are contained in the storagesection 59 a at one circumferential side and the storage section 59 b atthe other circumferential side of each insertion hole 59 respectively.Accordingly, no permanent magnet is located at a circumferentiallycentral portion of each insertion hole 59 where the magnetic directionis radial. Consequently, the thickness of the frame 52 can further bereduced.

It is considered that a radial dimension of the rotor core 53 could bereduced by employment of an anisotropic permanent magnet (plasticmagnet) in which the magnetic direction is a circumferential direction.However, the production cost of an anisotropic permanent magnet isdisadvantageously high. In the third embodiment, the ordinaryrectangular permanent magnets 60 are employed and accordingly, anincrease in the production cost can be prevented. Furthermore, the rotorcore 53 comprises a laminated iron core. Consequently, energy loss canbe reduced.

Furthermore, the frame 52 and the rotor core 53 are integrated by thesynthetic resin 35. In particular, the through holes 62 and the notches63 are formed in the rotor core 53 in the embodiment. These holes 62 andnotches 63 are filled with the synthetic resin 35. As a result, theframe 52 and the rotor core 53 can be integrated firmly. In this case,since the through holes 62 and the notches 63 are located at the outercircumferential side relative to the permanent magnets 60, the motorcharacteristics can be prevented from being adversely affected.Additionally, each insertion hole 59 is open at the outercircumferential face of the rotor core 53, whereas the upper and lowerends of each insertion hole 59 are closed. Consequently, each permanentmagnet can be prevented from being axially moved.

FIG. 15 illustrates a fourth embodiment of the invention. Only thedifference of the fourth embodiment from the third embodiment will bedescribed. The rotor core 53 comprises a plurality of unit cores 71which are connected into an annular configuration. Each unit core 71corresponds to a divided part of the core 53 including a plurality ofmagnetic poles. The unit cores 71 are connected to one another so that aconnection 71 a of the adjacent unit cores 71 is located between themagnetic poles as shown in FIG. 15. Consequently, the material for thecore 53 can efficiently be used. Moreover, since the connection 71 a islocated between the magnetic poles, the magnetic flux densitydistribution can be prevented from being adversely affected.

The rotor core 53 has a plurality of arc convex portions 30 formed on aninner circumferential face thereof except both circumferential ends ofeach magnetic pole. Each arc convex portion 72 is formed so that radialdimensions thereof at both circumferential ends thereof are smaller thana radial dimension thereof at the center thereof. The configuration,arrangement and dimensions of each convex portion 72 are set so that theair-gap magnetic flux density distribution is rendered substantiallysinusoidal. The configuration, arrangement and dimensions of each convexportion 72 were obtained from experiments carried out by the inventors.The above-described construction can improve the motor characteristics.

Furthermore, each storage section 59 a and 59 b has a widthsubstantially equal to or smaller than the thickness of the permanentmagnet 60, and the permanent magnets 60 are fitted into the storagesections 59 a and 59 b. Accordingly, no recesses 61 are formed in theouter periphery of each storage section 59 a and 59 b in the embodiment.Additionally, the rotor core 53 has no through holes 62 and no notches63 in the embodiment. When the frame 52 and the rotor core 53 areintegrated, the synthetic resin 35 fills each section of the innercircumferential face of the rotor core 53 between adjacent convexportions 72. Accordingly, the rotor core 53 can be fixed to the frame 52firmly even when the through holes 62 and the notches 63 are eliminated.Moreover, the inner circumferential face of the rotor core 53 can besmoothed since the synthetic resin 35 fills each section of the innercircumferential face of the rotor core 53 between adjacent convexportions 72. Accordingly, an increase in the noise due to rotation ofthe rotor 51 can be prevented by provision of the convex portions 72 onthe inner circumferential face of the core 53.

FIG. 16 illustrates a fifth embodiment of the invention. Only thedifference of the fifth embodiment from the first embodiment will bedescribed. In the fifth embodiment, protrusions 81 are provided near theopening 59 c of each insertion hole 59 so as to correspond to thestorage sections 59 a and 59 b respectively. The protrusions 81 protrudeto the outer circumferential side before insertion of the permanentmagnets into the respective storage sections 59 a and 59 b. After themagnets have been inserted in the respective storage sections 59 a and59 b, the protrusions 81 are bent thereby to depress the permanentmagnets 60 to the inner circumferential side. In this construction, too,the permanent magnets 60 can be positioned in the respective storagesections 59 a and 59 b.

Each permanent magnet 60 is formed into the rectangular plate shape inthe foregoing embodiments. As shown as a sixth embodiment in FIG. 17,however, a plurality of permanent magnets 91 each formed into the shapeof a generally arc plate may be used, instead. In this case, each onepermanent magnet 91 establishes one magnetic pole. In this embodiment,too, the thickness of the frame 52 can be reduced since the magneticdirection of each permanent magnet 51 is inclined circumferentially.

In the third to fifth embodiments, the frame need not be provided with afunction as the back yoke. Accordingly, the frame may be made ofplastic. Consequently, the weight of the rotor can further be reduced.

The foregoing description and drawings are merely illustrative of theprinciples of the present invention and are not to be construed in alimiting sense. Various changes and modifications will become apparentto those of ordinary skill in the art. All such changes andmodifications are seen to fall within the scope of the invention asdefined by the appended claims.

1. A rotor for a permanent magnet motor of an outer rotor type, therotor having a plurality of permanent magnets and disposed around astator, the rotor comprising: a frame; an annular iron core combinedintegrally with the frame; and a plurality of insertion holes formed inthe core so that the permanent magnets are inserted in the insertionholes respectively, wherein the frame, the core and the permanentmagnets are combined integrally with one another by a synthetic resin,and each insertion hole includes a magnet disposing portion in which thepermanent magnet is disposed, a space portion located in at least one ofcircumferential both ends of each permanent magnet disposed in themagnet disposing portion, and a positioning portion positioning eachpermanent magnet in the magnet disposing portion, and the moltensynthetic resin is poured into the space portion.
 2. A rotor for apermanent magnet motor of an outer rotor type, the rotor having aplurality of permanent magnets and disposed around a stator, the rotorcomprising: a frame; an annular iron core combined integrally with theframe; and a plurality of insertion holes formed in the core so that thepermanent magnets are inserted in the insertion holes respectively,wherein the frame, the core and the permanent magnets are combinedintegrally with each other by a synthetic resin, and each insertion holeincludes a magnet disposing portion in which the permanent magnet isdisposed and a recess defining a space along an outer periphery of eachpermanent magnet disposed in the magnet disposing portion, and themolten synthetic resin is poured into the recess.
 3. A rotor for apermanent magnet motor of an outer rotor type, the rotor having aplurality of permanent magnets and disposed around a stator, the rotorcomprising: a frame; an annular iron core combined integrally with theframe; and a plurality of insertion holes formed in the core so that thepermanent magnets are inserted in the insertion holes respectively,wherein the frame, the core and the permanent magnets are combinedintegrally with each other by a synthetic resin; the core has a throughhole from which a molten synthetic resin is poured; and a distance fromthe through hole to the outer circumference of the core is shorter thana distance from a axial center in a portion of the core where the corehas a maximum axial dimension, to the outer circumference of the core.4. A rotor for a permanent magnet motor of an outer rotor type, therotor having a plurality of permanent magnets and disposed around astator, the rotor comprising: a frame; an annular iron core combinedintegrally with the frame; and a plurality of insertion holes formed inthe core so that the permanent magnets are inserted in the insertionholes respectively, wherein the frame, the core and the permanentmagnets are combined integrally with each other by a synthetic resin;the core has a through hole from which a molten synthetic resin ispoured; and the through hole is formed nearer to the outer circumferenceof the core than the permenent magnets in the core.
 5. A rotor for apermanent magnet motor of an outer rotor type, the rotor having aplurality of permanent magnets and disposed around a stator, the rotorcomprising: a frame; an annular iron core combined integrally with theframe; and a plurality of insertion holes formed in the core so that thepermanent magnets are inserted in the insertion holes respectively,wherein the frame, the core and the permanent magnets are combinedintegrally with each other by a synthetic resin; the core has a throughhole from which a molten synthetic resin is poured; and the through holeis formed in the core so as to be located between the magnetic poles. 6.A rotor for a permanent magnet motor of an outer rotor type, the rotorhaving a plurality of permanent magnets and disposed around a stator,the rotor comprising: a frame; an annular iron core combined integrallywith the frame; a plurality of insertion holes formed in the core sothat the permanent magnets are inserted in the insertion holesrespectively, and a plurality of trough portions formed in the core soas to be located between the respective insertion holes adjacent to eachother in the inner circumferential portion thereof, the trough portionsbeing filled with a synthetic resin.
 7. The rotor according to claim 6,wherein a distance between an outer circumferential end of each troughportion and an outer circumferential portion of the core is smaller thana distance between a radial center of the core and the outercircumferential end of the core.